The invention relates to couplings in general, especially to pipe couplings, and more particularly to improvements in couplings of the type wherein an annular band-shaped housing surrounds the end portions of the objects to be coupled to each other and defines internal annular chambers or grooves for safety devices or gripping devices serving to penetrate into the material of the objects and to thereby hold the housing against slippage in the axial direction when the housing is tightened around the objects by means of screws, bolts and nuts or other clamping devices which reduce the width of the gap between the end portions of the housing. A coupling of the just outlined character is disclosed in the aforementioned copending patent application Ser. No. 079,659 to Zeidler now U.S. Pat. No. 4,819,974. The coupling of Zeidler further includes an elastic sleeve-like insert which is surrounded by the housing and, in turn, surrounds the end portions of the objects when the coupling is applied so that the insert establishes a reliable fluid-tight seal between the ends of the objects and the surrounding atmosphere. The housing of the coupling which is disclosed by Zeidler comprises two semicylindrical shells with radially outwardly extending flanges which are secured to each other by the aforementioned clamping devices. The shells are rigid castings, and they together form three internal annular grooves or chambers including two outer grooves for the safety devices and a central groove for the elastic insert. The width of the central groove (in the axial direction of the insert) is selected in such a way that a first marginal sealing lip of the insert surrounds the end portion of one object and a second marginal sealing lip of the insert surrounds the end portion of the other object. The median portion of the central groove is bounded by a cylindrical external surface and abuts a complementary cylindrical internal surface of the housing. The internal surface of the insert between the two marginal sealing lips is out of contact with the end portions of the objects, even when the clamping devices are applied to urge the lips into sealing engagement with the respective objects. This can present problems when the objects are fluid-conveying pipes and one of the pipes tends to change its inclination relative to the other pipe, i.e., when the axis of one of the pipes no longer coincides with but makes an angle of less than 180.degree. with the axis of the other pipe. The teeth which constitute the radially innermost portions of the sealing or gripping devices in the outer grooves of the housing then act not unlike pintles, and portions of the sealing lips are likely to become disengaged from the adjacent portions of external surfaces of the corresponding pipes. Such disengagement and resulting leakage of confined fluid into the surrounding atmosphere can take place even if the pressure in the space between the sealing lips of the insert is high or very high, i.e., even if the confined fluid tends to urge the lips into sealing engagement with the external surfaces of the pipes. In addition, when one of the pipes is caused to change its inclination relative to the other pipe, some of the teeth are likely to become disengaged from the respective pipe or pipes so that the coupling permits axial shifting of one of the pipes relative to the other pipe because the retaining or gripping action of the safety devices is insufficient to hold the pipes against axial movement relative to each other, for example, when such tendency of the pipes develops simultaneously with a change in orientation of one pipe relative to the other pipe.
British Pat. No. 911,358 to Victualic discloses a pipe joint wherein the central portion of an elastic sealing ring which is confined in a rigid metallic housing is spaced apart from the adjacent portions of peripheral surfaces of the pipes.
German Offenlegungsschrift No. 34 40 258 of Klingelhofer discloses a pipe coupling with a cylindrical housing which surrounds an elastic sealing sleeve.
German Offenlegungsschrift No. 34 43 943 of Hurter discloses a coupling which constitutes a modification of the coupling of Klingelhofer.
U.S. Pat. No. 2,459,251 to Stillwagon discloses a threadless pipe coupling wherein the central portion of an elastic sleeve, which is confined in a rigid housing, is spaced apart from the external surfaces of the pipes.
U.S. Pat. No. 2,225,208 to Crickmer discloses a pipe coupling which is similar to that of Stillwagon.